Övertonshalten i lågspänningsnätet : En studie i elkvalitet

All electrical loads need a power grid that delivers electricity with good quality. Current harmonics are a measure of how the electrical loads affect the power quality. Voltage harmonics are a measure on how the electrical loads are affected by the power quality and depend on both the power grid's strength and the current harmonics.This study examines and maps the harmonic voltages and currents in the low voltage grid by analysing 61 measurements which were done in Vattenfall’s electricity distribution grid during 2013. The study compiles guidelines and recommended levels for voltage harmonics in the low voltage grid from government agencies (Energimarknadsinspektionen), industry associations (CENELEC, Svensk Energi), companies (STRI) and Vattenfall’s planning levels and levels for good power quality . The study covers the guidelines and the recommended levels for current harmonics from government agencies (Elsäkerhetsverket), American and German engineering practices and from power grid companies (EON, Fortum and Öresundskraft). How the harmonic content in the 61 measurements relates to different values of voltage and current is also studied.The study suggests that there is reason to set requirements for the harmonics emission in customer agreements. The customers' current harmonics can be used in power quality analysis and in dialogue with customers. The trend among the recommended levels is that emission limit for current harmonics is based on the subscription's size alternatively maximum electrical load but also on network strength.The measurements indicate that the relationship between network strength and voltage harmonics is affected by the current harmonics such that a reduction of network strength does not increase the harmonic content of the voltage, which would have been expected. The relationship can be explained when voltage harmonics from a higher voltage levels dominate the voltage distortion in the low-voltage grid.The study indicates that the limits for voltage harmonics 15 and 21 are too low and should be revised. A method in question which is gaining attention is if it should be investigated further if it is more appropriate to use the 99 percentile values instead of 100 percentile in regulation 2013:1.Validerat; 20151016 (global_studentproject_submitter